1. Field of the Invention
The present invention relates to an electronic apparatus, such as an image pickup apparatus, for use with a removable storage medium, and a control method therefor, which are capable of reducing start-up time, and a program for implementing the method.
2. Description of the Related Art
Conventionally, there have been proposed electronic apparatuses in which a storage medium storing information can be removably mounted. In the following, a description will be given of an electronic apparatus of this kind by taking a portable digital camera as an example.
FIG. 27 is a block diagram showing the configuration of the conventional digital camera.
In FIG. 27, a RTC (Real Time Clock) 287 is a clock management device that manages time within a sub CPU 201 and the digital camera. Electric power is constantly supplied to the RTC 287 from a power supply 289. The sub CPU 201 is implemented by a low power consumption type. Connected to the sub CPU 201 are a RAM 205 for use by the sub CPU 201, a ROM 203 storing programs executed by the sub CPU 201, and an operation system 209 including a mode dial for use in designating an operation mode of the digital camera and various kinds of buttons. Further, a storage medium 271 implemented e.g. by a compact flash (registered trademark) for storing picked-up images is connected to the sub CPU 201, and a signal indicative of the status of attachment/detachment of the storage medium 271 is input to the sub CPU 201. The sub CPU 201 constantly monitors a signal indicative of the status of operation of the operation system 209 and the signal indicative of the status of attachment/detachment of the storage medium 271.
Further, the sub CPU 201 is connected to a power supply controller 281 to control electric power to be supplied to the overall system of the digital camera. Based on the monitored status of operation of the operation system 209, the sub CPU 201 determines whether an input instruction is for turning on the power supply 289 or for turning off the same, and then causes the power supply controller 281 to turn on or off the power supply 289. The power supply controller 281 is connected to the power supply 289 to extract voltages required for respective components of the digital camera from the voltage of the power supply 289 and then supply each of the voltages to a corresponding component. ON/OFF control of electric power supplied to each component is performed by the sub CPU 201.
A main CPU 245 has connected thereto a ROM 207 which stores programs according to which the main CPU 245 operates. The main CPU 245 reads out the programs from the ROM 207 and activates the same. Further, the main CPU 245 has connected thereto a RAM 217 which is a work memory for temporarily storing photographed image data and data necessary for operation of the main CPU 245.
Also connected to the main CPU 245 are a lens driver 219, an image pickup section 221 comprised of an image pickup device and a timing generator, an image display section 259 comprised of a LCD, and the storage medium 271. The lens driver 219, the image pickup section 221, the image display section 259, and the storage medium 271 are controlled by the main CPU 245 to perform intended processes. The sub CPU 201 and the main CPU 245 are connected to each other by communication means so as to detect each other's status. The main CPU 245 detects the status of operation of the operation system 209 using the communication means, determines an operation mode, such as a photographing mode or a playback mode, and carries out processing corresponding to the sensed operation mode.
Further, the main CPU 245 monitors the status of operation of the operation system 209 and the status of attachment/detachment of the storage medium 271 via the sub CPU 201. When an instruction for turning off the power is given via the operation system 209 in a state where the storage medium 271 is mounted, the main CPU 245 carries out processing for saving information of the file system and the like of the storage medium 271 in the RAM 217 and then executes a power-off process. Upon completion of the power-off process, the main CPU 245 notifies the sub CPU 201 of the completion.
When notified of the completion of the power-off process by the main CPU 245, the sub CPU 201 causes the power supply controller 281 to stop supply of electric power to the system of the digital camera. Even in the power-off state, the sub CPU 201 retains the history of the status of operation of the operation system 209 and that of the attachment/detachment of the storage medium 271. When a power-on operation is subsequently performed via the operation system 209, the sub CPU 201 turns on the power supply 289 via the power supply controller 281. As a result, electric power is supplied to the main CPU 245 to start up the same. When the storage medium 271 has remained mounted without being removed during the power-off state, the main CPU 245 reads out the information of the file system and the like of the storage medium 271, which has been saved in the RAM 217. Thus, time required for initialization of the storage medium 271 can be reduced. It is to be understood that when the storage medium 271 was removed and the same storage medium or a different one 271 was mounted during the power-off state, the mounted storage medium 271 is initialized.
The technique in which a sub CPU controls a power supply to manage electric power supplied to the overall system of a digital camera as described above has also been proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2002-237977.
However, it is necessary for an electronic apparatus of the above-described type, which is configured to constantly monitor the status of attachment/detachment of a storage medium, to incorporate not only a first CPU for controlling the overall operation of the apparatus, but also a second CPU (sub CPU) constantly supplied with electric power. This increases the member of component parts to complicate the circuit configuration of the apparatus and makes the apparatus expensive.
Further, recent electronic apparatuses have been more and more miniaturized, and accordingly each electronic apparatus tends to have a reduced device mounting area therein. This makes it difficult for such a miniaturized electronic apparatus to secure an area for mounting the second CPU in addition to the first CPU.
Furthermore, even when the main power supply of the electronic apparatus is off, it is necessary to constantly supply electric power to the CPU for monitoring the status of attachment/detachment of a storage medium. This increases power consumption, and if the electronic apparatus uses a battery as its power supply, the service life of the battery is shortened.
To overcome this problem, recently, low power consumption CPUs have been developed. Nevertheless, the amount of electric power required for driving the low power consumption CPUs is larger than that of electric power consumed by low power consumption devices, such as a RTC. Therefore, electronic apparatuses having incorporated therein a low power consumption CPU which is always driven in the power-off status of the apparatuses consume a larger amount of electric power than apparatuses without a CPU being always driven.
On the other hand, to give top priority to reduction of power consumption and extension of the service life of the battery, if monitoring of the status of attachment/detachment of the storage medium is stopped when the main power supply of the electronic apparatus is off, it is necessary to acquire information of the storage medium whenever the apparatus is started up, which causes an increase in start-up time. In general, with an increase in the capacity of a storage medium, time necessary for initialization increases. In recent years, the increase in the capacity of storage media has been marked, and this trend will continue undoubtedly. Therefore, it can be easily foreseen that start-up time will be more and more increased.
Further, even when the main power supply of the electronic apparatus is off, the status of attachment/detachment of the storage medium is monitored by the monitoring CPU supplied with electric power from an auxiliary power supply to detect whether or not the storage medium has been removed from the apparatus. However, if the electronic apparatus is brought into a state where the monitoring CPU cannot be supplied with electric power from either the main power supply or the auxiliary power supply, the status of attachment/detachment of the storage medium cannot be monitored from then on. If the storage medium is removed under this situation, this can cause wrong attachment/detachment history information indicative of the status of attachment/detachment of the storage medium. To avoid this, the attachment/detachment history information of the storage medium has to be checked whenever the electronic apparatus is started up.